How does a star blow up?

Apparently the supernova simulation folks have been having some problems getting the simulations to go bang reliably: "the main shock wave often stalls out and the star fails to shatter."

I wasn't aware of that little problem, and my reaction is "OK, something is missing in your model."

Maybe what was missing was simple. The NuSTAR telescope was designed to distinguish the X-rays associated with the decay of radioactive elements. Since radioactive elements are largely produced in the hot cores of stars, not the outer layers, the distribution of elements around a relatively recent supernova should tell something about what the core looked like as it went bang. For example, are there jets coming out of the top and bottom?

“Stars are spherical balls of gas, and so you might think that when they end their lives and explode, that explosion would look like a uniform ball expanding out with great power,” said Fiona Harrison, the principal investigator of NuSTAR at the California Institute of Technology (Caltech) in Pasadena. “Our new results show how the explosion’s heart, or engine, is distorted, possibly because the inner regions literally slosh around before detonating.”

Go look at the pictures showing the distributions of different isotopes. They aren't very uniform.